Detection method of silicon controlled rectifier (thyristor)-EEWORLD

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The international general name of silicon controlled rectifier (SCR) is Thyyistoy, which is abbreviated as thyristor in Chinese. It can work under high voltage and high current conditions, and has the advantages of high withstand voltage, large capacity and small size. It is a high-power switching semiconductor device and is widely used in power and electronic circuits. 1. Characteristics of silicon controlled rectifier. Silicon controlled rectifiers are divided into unidirectional silicon controlled rectifiers and bidirectional silicon controlled rectifiers. Unidirectional silicon controlled rectifiers have three lead pins: anode A, cathode K, and control electrode G. Bidirectional silicon controlled rectifiers have three lead pins: first anode A1 (T1), second anode A2 (T2), and control electrode G. Only when a positive voltage is applied between the anode A and cathode K of the unidirectional silicon controlled rectifier, and the required positive trigger voltage is applied between the control electrode G and the cathode, can it be triggered to conduct. At this time, A and K are in a low-resistance conduction state, and the voltage drop between the anode A and the cathode K is about 1V. After the unidirectional thyristor is turned on, even if the controller G loses the trigger voltage, as long as the positive voltage is maintained between the anode A and the cathode K, the unidirectional thyristor continues to be in the low-resistance conduction state. Only when the voltage of anode A is removed or the voltage polarity between anode A and cathode K changes (AC zero crossing), the unidirectional thyristor is converted from the low-resistance conduction state to the high-resistance cut-off state. Once the unidirectional thyristor is cut off, even if the positive voltage is reapplied between anode A and cathode K, it is still necessary to reapply the positive trigger voltage between the control electrode G and cathode K before it can be turned on. The conduction and cut-off states of the unidirectional thyristor are equivalent to the closed and open states of the switch, and it can be used to make a contactless switch. Between the first anode A1 and the second anode A2 of the bidirectional thyristor, no matter whether the voltage polarity is forward or reverse, as long as a trigger voltage with different positive and negative polarities is applied between the control electrode G and the first anode A1, it can be triggered to conduct in a low-resistance state. At this time, the voltage drop between A1 and A2 is also about 1V. Once the bidirectional thyristor is turned on, it can continue to remain in the on state even if the trigger voltage is lost. The bidirectional thyristor is cut off only when the current of the first anode A1 and the second anode A2 decreases and is less than the holding current or when the voltage polarity between A1 and A2 changes and there is no trigger voltage. At this time, it can only be turned on by reapplying the trigger voltage. 2. Detection of unidirectional thyristor. Select the resistance R*1Ω block on the multimeter, and use the red and black test pens to measure the forward and reverse resistance between any two pins until a pair of pins with a reading of tens of ohms is found. At this time, the pin of the black test pen is the control electrode G, the pin of the red test pen is the cathode K, and the other empty pin is the anode A. At this time, connect the black test pen to the determined anode A, and the red test pen is still connected to the cathode K. At this time, the pointer of the multimeter should not move. Use a short wire to short-circuit the anode A and the control electrode G instantly. At this time, the pointer of the multimeter resistance block should deflect to the right, and the resistance reading is about 10 ohms. If the anode A is connected to the black test lead and the cathode K is connected to the red test lead, the multimeter pointer deflects, indicating that the thyristor has been broken down and damaged.

Reference address：Detection method of silicon controlled rectifier (thyristor)

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